Multi-junction pv module

ABSTRACT

A photovoltaic device is provided which includes a plurality of junction layers. Each junction layer includes a plurality of photovoltaic cells electrically connected to one another. At least one of the junction layers is at least in part optically transmissive. The junction layers are arranged in a stack on top of each other.

BACKGROUND

1. Field

The present invention relates generally to a method of manufacturingthin-film photovoltaic devices, and particularly to a method for themanufacturing of high-efficiency thin-film photovoltaic devices.

2. Related Art

Photovoltaic devices represent one of the major sources ofenvironmentally clean and renewable energy. They are frequently used toconvert optical energy into electrical energy. Typically, a photovoltaicdevice is made of one semiconducting material with p-doped and n-dopedregions. The conversion efficiency of solar power into electricity ofthis device is limited to a maximum of about 37%, since photon energy inexcess of the semiconductor's bandgap is wasted as heat. A photovoltaicdevice with multiple semiconductor layers of different bandgaps is moreefficient: an optimized two-bandgap photovoltaic device has the maximumsolar conversion efficiency of 50%, whereas a three-bandgap photovoltaicdevice has the maximum solar conversion efficiency of 56%. Realizedefficiencies are typically less than theoretical values in all cases.

Multi-layered or multi-junction devices are currently manufactured asmonolithic wafers, where each semiconductor layer is crystal-grown ontop of the previous one. As a result, the semiconductor junction layersare electrically connected in series and have to be current-matched, inorder to obtain maximum conversion efficiency. This current-matchingprocedure complicates the design and decreases the efficiency of thedevice. The latter becomes particularly evident when considering theeffect of spectral filtering on the device efficiency. If a part of thesolar spectrum is absorbed or scattered, e.g. by water vapors, theresulting disproportional decrease of photocurrent in one of junctionswill limit the current through the whole device and thus decrease itsconversion efficiency.

SUMMARY

In accordance with the present invention, a photovoltaic device isprovided which includes a plurality of junction layers. Each junctionlayer includes a plurality of photovoltaic cells electrically connectedto one another. At least one of the junction layers is at least in partoptically transmissive. The junction layers are arranged in a stack ontop of each other.

In accordance with one aspect of the invention, each of the junctionlayers comprises at least one pair of electrical terminals for producingphotogenerated current.

In accordance with another aspect of the invention, the junction layersare manufactured separately on separate substrates.

In accordance with another aspect of the invention, the junction layersare laminated to each other.

In accordance with another aspect of the invention, the junction layersare produced on a common substrate.

In accordance with another aspect of the invention, the junction layersare electrically insulated from each other.

In accordance with another aspect of the invention, the plurality ofjunction layers comprises at least first and second junction layers. Thefirst layer is configured to absorb a first portion of incident lightenergy and transmit a second portion of the incident light energy to thesecond junction layer and the second junction layer is configured toabsorb at least a portion of the second incident light energy.

In accordance with another aspect of the invention, the first junctionlayer comprises photovoltaic cells with a characteristic bandgap that islarger than that of cells in the second junction layer.

In accordance with another aspect of the invention, a number of thephotovoltaic cells in at least two of the junction layers are chosen sothat their respective output voltages are about equal.

In accordance with another aspect of the invention, a number of thephotovoltaic cells in at least two of the junction layers are chosen sothat their respective output currents are about equal.

In accordance with another aspect of the invention, at least two of thejunction layers are electrically connected in parallel.

In accordance with another aspect of the invention, at least two of thejunction layers are electrically connected in series.

In accordance with another aspect of the invention, at least one of thejunction layers is produced from photovoltaic cells based on CIGSalloys.

In accordance with another aspect of the invention, n at least one ofthe junction layers is produced from photovoltaic cells based on CdTealloys.

In accordance with another aspect of the invention, at least one of thejunction layers is produced from photovoltaic cells based on Si alloys.

In accordance with another aspect of the invention, electrical leads areconnected to the electrical terminals.

In accordance with another aspect of the invention, a junction box isprovided with connectors connected to the electrical leads.

In accordance with another aspect of the invention, high currentprotection diodes are provided.

In accordance with another aspect of the invention, the photovoltaiccells in each junction layer are electrically connected to one anotherin series.

In accordance with another aspect of the invention, a method ofproducing a multi-junction layer photovoltaic device includes forming afirst junction layer by producing a first set of individual photovoltaiccells on a substrate and electrically interconnecting them to oneanother. A second junction layer is formed by producing a second set ofindividual photovoltaic cells and electrically interconnecting thephotovoltaic cells in the second set to one another. The first junctionlayer is attached to the second junction layer.

In accordance with another aspect of the invention, the second junctionlayer is formed on a second substrate prior to attaching the firstjunction layer to the second junction layer.

In accordance with another aspect of the invention, an insulation layeris formed between the first and second junction layers.

In accordance with another aspect of the invention, a method ofproducing a multi-junction layer photovoltaic device includes forming afirst junction layer by producing a first set of individual photovoltaiccells on a substrate and electrically interconnecting them to oneanother. An insulation layer is formed above the first junction layerand a second junction layer is formed above the insulation layer byproducing a second set of individual photovoltaic cells and electricallyinterconnecting the photovoltaic cells in the second set to one another.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a typical PV module.

FIG. 2 is a typical monolithically integrated PV module.

FIG. 3 is a typical monolithically integrated multi-junction PV module.

FIG. 4 is a typical multi-junction PV cell.

FIG. 5 is a two-junction-layer PV module.

FIG. 6 is a three-junction-layer PV module.

FIG. 7 is a monolithically integrated two-junction-layer PV module.

FIG. 8 is a two-junction-layer PV module with external electrical leads.

FIG. 9 is a schematic of m-junction-layer PV module with parallelinterconnections.

FIG. 10 is a schematic of m-junction-layer PV module with serialinterconnections.

FIG. 11 is a schematic of m-junction-layer PV module with parallel andserial interconnections.

FIG. 12 is a plot of current vs. voltage for three junction layers (I1,I2 and I3) and their total current (I) in a three-junction PV module,where junction layers have been voltage-matched.

FIG. 13 is a plot of current vs. voltage for three junction layers (V1,V2 and V3) and their total current (V) in a three-junction PV module,where junction layers have been current-matched.

FIG. 14 is a schematic of two-junction-layer PV module with parallelinterconnections.

FIG. 15 is a schematic of two-junction-layer PV module with serialinterconnections.

FIG. 16 is a schematic of two-junction-layer PV module with serialinterconnections.

FIG. 17 is a schematic of m-junction-layer PV module with parallelinterconnections and high current protection diodes.

FIG. 18 is a schematic of m-junction-layer PV module with serialinterconnections and high current protection diodes.

FIG. 19 is the backside of a two-junction layer PV module with externalleads and a junction box.

FIG. 20 is a junction box for a two-junction layer PV module withparallel interconnections.

FIG. 21 is a junction box for a two-junction layer PV module with serialinterconnections.

FIG. 22 shows junction layers that are respectively composed of cellselectrically interconnected in series (A), in parallel (B) andindependently connected (C).

DETAILED DESCRIPTION Overview

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of exemplaryembodiments or other examples described herein. However, it will beunderstood that these embodiments and examples may be practiced withoutthe specific details. In other instances, well-known methods,procedures, components and circuits have not been described in detail,so as not to obscure the following description. Further, the embodimentsdisclosed are for exemplary purposes only and other embodiments may beemployed in lieu of, or in combination with, the embodiments disclosed.

As summarized above and described in more detail below, the apparatusfor efficient photovoltaic energy conversion device and the method forproducing the same is provided. Embodiments of this apparatus and methodmay facilitate the ability to efficiently and economically convertelectromagnetic energy in the form of light into electrical energy inthe form of electrical current. Embodiments of this apparatus and methodmay also facilitate large volume production and widespread usage ofphotovoltaic devices.

This invention provides thin-film technology as an alternative means ofproducing a multi-junction photovoltaic device. As well known in theart, multi-junction devices in general are more efficient for conversionsolar energy into electricity than regular PV devices. However, thedevelopment of these devices is currently hindered by the complexity ofsemiconductor manufacturing processes and their high cost. On the otherhand, thin-film processing is substantially less complex and expensive.Using new design approaches and thin-film technology, a new efficientphotovoltaic device with expanded capabilities and application range canbe produced.

Typically, single-crystal semiconductors are grown epitaxially,layer-by-layer on a monolithic wafer. Thin-film materials, in contrast,depending on their chemical origin can be deposited and layered by avariety of different methods, using for example evaporation, sputtering,spraying, inkjet printing etc., some of which could be very inexpensive.Furthermore, some thin-film layers can be produced separately and thenintegrated hybridly using bonding, lamination and other similar methods.Alternatively, in some cases the entire structure may be sequentiallygrown without the need for any mechanical integration of the individuallayers. This flexibility in a manufacturing method makes it possible toimplement new design approaches in producing a better photovoltaicdevice.

A typical photovoltaic (PV) module 100 shown in FIG. 1 includes severalPV cells 110, which are interconnected electrically in series by tabs120. As a result, all photovoltaic power may be extracted at a single apair of terminals 130. Module 100 may also include a carrier 140 toprovide mechanical support for PV cells 110. In this approach cells 110are produced separately and then manually interconnected with each otherto produce a so-called string of cells. Crystalline silicon PV modules,for example, are usually produced using this approach. Alternatively, amonolithically integrated module 200 may be produced as shown in FIG. 2,in which individual cells 210 are produced simultaneously on the samesubstrate 240 and interconnected using thin-film layers 220 to form astring of cells with a single pair of terminals 230. This manufacturingapproach may be used in fabrication of CdTe-based PV modules, forexample. In both cases, however, individual cells 110 and 210,respectively, are single-junction cells. Such cells are less efficientin comparison with multi-junction cells.

Strings and modules based on multi-junction cells have also beenproduced using similar approaches. FIG. 3 shows a PV module 300, whereinstead of single junction cells, multi-junction cells 310 aremonolithically integrated using thin-film interconnections 320 toproduce a string of cells 310 with a single pair of terminals 330. Thecells 310 are formed on substrate 340. This approach is used, forexample, by United Solar to produce modules with triple-junction a-Sicells. In this case, a triple-junction cell 400, which is shown in FIG.4, includes substrate 401, back contact 410, first p-type semiconductorlayer 421, first n-type semiconductor layer 422, buffer layer 430,second p-type semiconductor layer 441, second n-type semiconductor layer442, buffer layer 450, third p-type semiconductor layer 461, thirdn-type semiconductor layer 462 and top contact 470. First, second andthird junctions are produced between respective p-type and n-typesemiconductor layers based on a-Si. The buffer layers provide mechanicaland electrical connection between the junctions so that they areconnected in series and thus the same electrical current flows througheach layer in cell 400. This condition, called current matching, limitsthe performance of a multi-junction cell and reduces its powerconversion efficiency.

As shown in FIG. 5, the present invention provides a different method ofproducing a multi-junction PV module. PV module 500 is produced bystacking and attaching at least two junction layers 510 and 520. In thisparticular example both junction layers 510 and 520 are stringscomprised of PV cells electrically connected in series. Individual cells512 in PV string 510 and cells 522 in PV string 520 may beinterconnected using monolithic integration as shown in FIG. 5.Alternatively, other interconnection methods may be used as well,including tabbing or tiling of individual cells. The PV strings may beproduced independently from each other on individual substrates 511 and521, respectively. Strings 510 and 520 may also have individualterminals 515 and 525 for electrical connections. These terminals may beused either for internal or external connections, as discussed below.Protective coatings 513 and 514 may be used to cover PV strings cells512 and 522, respectively, to improve device reliability and providemechanical connection. Additional junction layers may be produced usingthis method, increasing the total number of junction layers to more thantwo. For instance, FIG. 6 shows a three-junction PV module composed ofthree individual strings 610, 620 and 630.

While the example in FIG. 5 shows a pair of junction layers that areformed from strings of cells, the concept of a junction layer may begeneralized, as will be explained with reference to FIGS. 22 a-22(c). Ingeneral, a junction layer may include a plurality of individual PV cellsthat are electrically connected to one another in any of a variety ofdifferent ways. For instance, in FIG. 22( a) junction layer 2210 mayinclude cells 2211 connected in series and a single pair of outputterminals 2212. In FIG. 22( b), on the other hand, junction layer 2220may include cells 2221 connected in parallel and a single pair of outputterminals 2222. In FIG. 22( c) junction layer 2230 may include cells2231 independently connected to a plurality of individual outputterminals 2232.

As previously noted, in one aspect of the invention, a junction layer ina multi-junction PV module may be composed of a number of PV cells thatare interconnected together to form a PV string. The individual PV cellsmay be single- or multi-junction cells. In the latter case, amulti-junction PV cell may be a typical multi-junction cell, in whichjunctions are physically and electrically connected in series (e.g. PVcell 400). Two or more such strings may be stacked on top of each otherto produce a multi-junction PV module (e.g. module 500). The upperjunction layers, or strings, (e.g. string 520) may be at least partiallytransparent. The numbers of cells in each string (e.g. 510 and 520) maybe the same or different. Furthermore, PV cells in different strings(e.g., cells 512 and 522) may be produced using absorber materials withdifferent characteristic bandgaps. In this case the cells in the upperstring (string 520) may have a larger bandgap absorber as compared tothat of the cells in the lower string (string 510). In this case thecells in the upper string, i.e. the upper junction layer, face the lightsource, absorb the first portion of the light and transmit the rest tothe bottom cells.

In yet another aspect of the invention, a multi-junction PV module isproduced in which each junction layer contains multiple PV cellsdirectly connected with each other in series and forming at least one PVstring. There may be at least two junction layers, and the upperjunction layers may be at least partially transparent. It may bepreferred to produce PV cells in different junction layers fromdifferent absorber materials, so that the absorber bandgap of a cell inthe upper junction layer may be larger than the bandgap of the lowerjunction layer or layers. There also may be a preferred set of absorberbandgaps for the junction layers that maximizes the power conversionefficiency of a multi-junction PV module.

The junction layers may be produced separately on separate substrates ormonolithically on the same substrate. In the latter case, as shown inFIG. 7, the cells in each junction layer may be interconnectedmonolithically into a string. Common substrate 711 is used to first growa series of cells 712 interconnected to produce string 710 and then growa series of cells 722 interconnected to produce string 720. Additionalinsulating and protective layers 713 and 723 may be grown on top ofstrings 710 and 720, respectively. Respective electrical contacts 715and 725 may be produced at the edges. For instance multi-junction PVmodule based on a-Si and SiGe alloys may be produced using this method.Also, in addition to thin-film deposition techniques other techniquesmay be used, such as epitaxial growth of III-V type semiconductors, forexample.

In another aspect of the invention, the characteristics of each junctionlayer in a multi-junction PV module may be designed and produced in sucha way so as to match them and enable electrical interconnection withoutthe use of other electrical conversion circuits. FIG. 9 shows a parallelinterconnection of junction layers in an m-junction layer PV module. Inthis case, the number of cells in each junction layer may be selected sothat each layer produces about the same output voltage. Alternatively,FIG. 10 shows an in-series interconnection of junction layers in anm-junction layer PV module. In this case, the number of cells in eachjunction layer may be selected so that each layer produces about thesame output current. FIG. 11 shows a hybrid interconnection of junctionlayers, in which both types of connections (in parallel and in series)may be used.

For example, in module 600 shown in FIG. 6, junction layers 610, 620 and630 may be produced having different current-voltage (IV)characteristics with corresponding sets of open circuit voltage(V_(oc)), short circuit current (I_(sc)) and maximum power voltage(V_(m)) and current (I_(m)) under typical illumination conditions. I-Vcharacteristics may be matched so that each junction layer producesnearly the same output voltage (voltage matching: V₁=V₂=V₃, as shown inFIG. 12) or nearly the same output currents (current matching: I₁=I₂=I₃,as shown in FIG. 13). In this case junction layers 610, 620 and 630 maybe interconnected either in parallel (for voltage-matched junctionlayers) or in series (for current-matched junction layers) usingcorresponding electrical output terminals. Other interconnection schemesbetween three junction layers may be used. For example, junction layers610 and 620 may be current matched and interconnected in series.Junction layer 630 in turn may be voltage matched and connected inparallel to the in-series interconnected layers 610 and 620. Electricalinterconnections may be achieved using either internal connectionsinside a PV module or external connectors accessible from the outside ofa PV module.

The devices, apparatus and methods described herein provide technicalbenefits and advantages that are currently not achieved withconventional technologies. For example, new module designs may beproduced in which a multi-junction PV module is subdivided into multiplejunction layers with independent output terminals. Alternatively, a newdesign may be produced in which some cells and junction layers may beconnected in series with better current matching characteristics andtherefore higher conversion efficiency than standard designs. Thisadvantage may be realized because the current matching condition in thiscase is established between whole junction layers rather than individualcells. Also, parallel interconnections become possible in this newdesign approach, since such interconnections occur between junctionlayers rather than individual cells and therefore not only current butalso voltage matching conditions can be achieved. The invention can alsogreatly facilitate manufacturing of multi-junction modules by, amongother things, improving manufacturing yield and enabling new PVtechnologies. Individual junction layers may be inspected and testedbefore the final assembly of a multi-junction PV module, thus avoidingthe risk of using a nonperforming cell in the assembly Furthermore,different PV technologies may be used and mixed in the manufacturing ofsuch a multi-junction PV module, which may lower manufacturing costs andincrease performance.

EXAMPLES

In one embodiment of this invention, a two junction layer PV module maybe produced as shown in FIG. 8. Bottom junction layer 810 may be made ofseveral thin-film cells 812, which are monolithically integrated andconnected electrically in series to form a single string. Correspondingthin-film semiconductor absorber material may be based on CuInSe₂compound and its alloys with Ga and S, more commonly known in theindustry as CIGS. Similarly, top junction layer 820 may be also made ofseveral CIGS-based cells 822, which are monolithically integrated andconnected electrically in series into a single string. It may bepreferred to adjust the CIGS compositions of cells 812 and 822 so thattheir respective optical bandgaps are about 1.1 eV and 1.7 eV. Therespective compositions of cells 812 and 822 in this case may be closeto CuIn_(0.8)Ga_(0.2)Se₂ and CuGaSe₂, for instance. Monolithicintegration of these CIGS cells may be accomplished by laser andmechanical scribing. The top junction layer (layer 820) may be producedon a transparent substrate 821, such as soda lime glass (SLG) orpolyimide. Furthermore, back contacts used in cells 822 may be alsotransparent, such as for example doped tin oxide or indium tin oxide.The bottom junction layer (layer 810) may be produced on similarsubstrates or other types of substrates, for example stainless steel oraluminum foil. Junction layers 810 and 820 may be laminated together toproduce two junction layer PV module 800. An additional adhesion layer813, such as a silicone layer, may be used to attach the two layers.Individual contact pairs 815 and 825 may be provided for both junctionlayers. Additional insulating layers 814 may be used to provideelectrical separation between these contacts.

In another embodiment, a three-junction PV module may be produced usingthree different types of CIGS cells. It may be preferred to have bottom,middle and top junction layers with cells having corresponding CIGScompositions close to CuInSe₂, CuIn_(0.7)Ga_(0.3)S_(0.6)Se_(1.4) andCuIn_(0.3)Ga_(0.7)SeS, respectively. These compositions in turn producesemiconductors with characteristic bandgaps of about 1 eV, 1.35 eV and1.8 eV.

In another embodiment, a multi-junction PV module may be produced usingjunction layers comprising cells based on CIGS alloys with Al, Te orother elements.

In another embodiment, a multi-junction PV module may be produced usingjunction layers comprising cells based on CdTe alloys, such asCd_(1-x)Hg_(x)Te, Cd_(1-x)Mn_(x)Te, Cd_(1-x)Zn_(x)Te, Cd_(1-x)Mg_(x)Te,and others.

In another embodiment, a multi-junction PV module may be produced usingjunction layers comprising cells based on Si, Si:H, Si:C and Si:Gealloys, either in polycrystalline, micro-crystalline, nanocrystalline oramorphous form.

In another embodiment, a multi-junction PV module may be produced usingjunction layers comprising dissimilar materials, e.g. CIGS, CdTe, Ge andothers.

In another embodiment, a multi-junction PV module may be produced byaligning and joining junction layers, so that the scribing lines arealigned between the adjacent layers (e.g. module 600 in FIG. 6).

In another embodiment, a two-junction PV module 1400 may be produced asshown in FIG. 14, in which the two junction layers 1410 and 1420 arecomprised of cells 1411 and 1421, respectively, having different outputvoltages, e.g. V_(top) and V_(bottom). The number of cells in thejunction layers may be chosen so that the layers' output voltages areabout the same, i.e. V_(out)=NV_(top)=MV_(bottom). In this case, the twojunction layers may be connected in parallel, i.e. terminal 1412connects to terminal 1422 and terminal 1413 connects to terminal 1423.Of course, similarly a three-junction or N-junction PV module may beproduced, in which at least some junction layers are connected inparallel. In this particular case, the mutual orientations of thejunction layers may be the same as shown in FIG. 14 (sides with samepolarity face the same way), which is convenient for parallelinterconnections.

In another embodiment, a two-junction PV module 1500 may be produced asshown in FIG. 15, in which the two junction layers 1510 and 1520 arecomprised of cells 1511 and 1521, respectively, having different outputcurrents, e.g. I_(top) and I_(bottom). The number of cells in thejunction layers may be chosen so that the layer output currents areabout the same. In this case, the two junction layers may be connectedin series, i.e. terminal 1523 connects to terminal 1522. Of course,similarly a three- or more layered junction PV module may be produced,in which at least some junction layers are connected in series. In thisparticular case, the mutual orientation of the junction layers may bethe same as shown in FIG. 15. Alternatively and more preferably,junction layers may be oriented opposite of each other as shown in FIG.16, which is more convenient for in-series layer interconnections. Inthis case, the output polarities of the adjacent junction layers arereversed, so that the positive terminal 1612 of junction layer 1610 ison the same side next to the negative terminal 1622 of junction layer1620 and visa versa.

In another embodiment, a multi-junction PV module may be producedcomprised of multiple junction layers, at least some of which includebypass diodes for protection against either reverse current or voltage.For example, FIG. 17 shows an m junction layer PV module, in which thejunction layers are connected in parallel and each one of them has ablocking diode connected in series for protection against a high reversecurrent. Also, FIG. 18 shows an m junction layer PV module, in which thejunction layers are connected in series and each one of them has abypass diode connected in parallel for protection against a high forwardcurrent.

In another embodiment, a two junction layer PV module 1900 may beproduced as shown in FIG. 19, in which the terminals from each junctionlayer are connected to wrap-around leads 1930 that in turn connect torespective terminals in a junction box 1940.

In another embodiment, a two junction layer PV module may comprise twojunction layers connected in parallel. The junction interconnection maybe external and occur inside the junction box 2000 shown in FIG. 20. Inthis case the junction box provides easy access to the connections 2020and other terminals and in particular, terminals 2040 for connectingcurrent-blocking protection diodes 2030. The diodes may be easilyreplaced if necessary.

In another embodiment, a two junction layer PV module may comprise twojunction layers connected in series. The junction interconnection may beexternal and occur inside the junction box 2100 shown in FIG. 21.Similarly, a multi-junction PV module with more than two junction layersmay be provided with a junction box and corresponding connectionterminals.

In another embodiment, a multi-junction PV module may be produced usinga non-planar substrate, for example cylindrical, spherical, orarbitrarily shaped. Junction layers may be successively attached orlaminated onto such a substrate.

Variations of the apparatus and method described above are possiblewithout departing from the scope of the invention.

1. A photovoltaic device comprising a plurality of junction layers, eachjunction layer comprising a plurality of photovoltaic cells electricallyconnected to one another; at least one of said junction layers being atleast in part optically transmissive; and said junction layers arrangedin a stack on top of each other.
 2. The photovoltaic device of claim 1wherein each of said junction layers comprises at least one pair ofelectrical terminals for producing photogenerated current.
 3. Thephotovoltaic device of claim 1 wherein said junction layers aremanufactured separately on separate substrates.
 4. The photovoltaicdevice of claim 1 wherein said junction layers are laminated to eachother.
 5. The photovoltaic device of claim 1 wherein said junctionlayers are produced on a common substrate.
 6. The photovoltaic device ofclaim 1 wherein said junction layers are electrically insulated fromeach other.
 7. The photovoltaic device of claim 1 wherein said pluralityof junction layers comprises at least first and second junction layers,the first layer being configured to absorb a first portion of incidentlight energy and transmit a second portion of the incident light energyto the second junction layer, the second junction layer being configuredto absorb at least a portion of the second incident light energy.
 8. Thephotovoltaic device of claim 7 wherein said first junction layercomprises photovoltaic cells with a characteristic bandgap that islarger than that of cells in said second junction layer.
 9. Thephotovoltaic device of claim 1 wherein a number of said photovoltaiccells in at least two of the junction layers are chosen so that theirrespective output voltages are about equal.
 10. The photovoltaic deviceof claim 1 wherein a number of said photovoltaic cells in at least twoof the junction layers are chosen so that their respective outputcurrents are about equal.
 11. The photovoltaic device of claim 2 whereinat least two of the junction layers are electrically connected inparallel.
 12. The photovoltaic device of claim 2 wherein at least two ofthe junction layers are electrically connected in series.
 13. Thephotovoltaic device of claim 1 wherein at least one of the junctionlayers is produced from photovoltaic cells based on CIGS alloys.
 14. Thephotovoltaic device of claim 1 wherein at least one of the junctionlayers is produced from photovoltaic cells based on CdTe alloys.
 15. Thephotovoltaic device of claim 1 wherein at least one of the junctionlayers is produced from photovoltaic cells based on Si alloys.
 16. Thephotovoltaic device of claim 2 further comprising electrical leadsconnected to said electrical terminals.
 17. The photovoltaic device ofclaim 16 further comprising a junction box with connectors connected tosaid electrical leads.
 18. The photovoltaic device of claim 17 furthercomprising high current protection diodes.
 19. The photovoltaic deviceof claim 1 wherein the photovoltaic cells in each junction layer areelectrically connected to one another in series.
 20. A method ofproducing a multi-junction layer photovoltaic device comprising: forminga first junction layer by producing a first set of individualphotovoltaic cells on a substrate and electrically interconnecting themto one another; and forming a second junction layer by producing asecond set of individual photovoltaic cells and electricallyinterconnecting the photovoltaic cells in the second set to one another;and attaching the first junction layer to the second junction layer. 21.The method of claim 20 wherein the second junction layer is formed on asecond substrate prior to attaching the first junction layer to thesecond junction layer.
 22. The method of claim 21 further comprisingforming an insulation layer between the first and second junctionlayers.
 23. A method of producing a multi-junction layer photovoltaicdevice, comprising: forming a first junction layer by producing a firstset of individual photovoltaic cells on a substrate and electricallyinterconnecting them to one another; and forming an insulation layerabove the first junction layer; and forming a second junction layerabove the insulation layer by producing a second set of individualphotovoltaic cells and electrically interconnecting the photovoltaiccells in the second set to one another.